A THEORETICAL INVESTIGATION OF THE EFFECT OF MATERIAL PROPERTIES AND CAVITY ARCHITECTURE SHAPE ON DUCTILE FAILURE DURING THE HOT TENSION TEST/

The effect of material properties and cavity architecture, shape, and orientation on ductile failure behavior during hot tension testing was established using a numerical analysis of the deformation of a repres entative ''microspecimen.'' The microspecimen consisted of two regions , or slices, one containing the cavities and the other comprising a un iform, cavity-free area. The cavities were assumed to be spherical or cylindrical and to form a simple cubic (sc), body-centered cubic (bcc) , or face-centered cubic (fcc) network; tensile loading was taken to b e parallel to either the cube edge, face diagonal, or body diagonal. B y invoking load equilibrium, expressions describing the relation betwe en the deformations in the uniform and cavity-containing regions were derived. The principal material-related coefficients in these equation s were a geometry factor G, whose value depended on the specific cavit y architecture and tensile loading direction, the strain-hardening and strain-rate sensitivity exponents n and m, and the parameter eta, use d to describe the (volumetric) cavity growth kinetics. For cylindrical cavities, the pertinent void-growth parameter was deduced to be the a rea cavity growth rate eta(A). Failure was predicted to be either reta rded or accelerated when eta(A) is less than or greater than 2 eta/3, respectively. The simulations were used to quantify the microscopic st rain localization kinetics and, thus, to identify those deformation re gimes in which void growth vs void coalescence (i.e., ''internal necki ng'') predominates during the ductile failure process. Model predictio ns of tensile elongation were validated by comparison with experimenta l measurements for cavitating materials found in the literature.